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WASHINGTON — Rates for cancer cases and deaths went down in the 1990s, led by declines for prostate, lung and colon cancer, according to combined government and private studies. More breast cancer cases were detected, apparently because of aggressive screening.

“This is an optimistic report because overall cancer rates are tending toward a decline,” said Holly L. Howe, one of the authors of a report appearing Wednesday in the Journal of the National Cancer Institute.

The big four killer cancers – breast, prostate, lung and colon-rectum – accounted for 52.7 percent of the 1998 cancer deaths in the U.S., the study found. These diseases also accounted for 55.9 percent of all new cancers.

Death rates for eight of the top 10 cancers were all level or declining. The exceptions were the death rates for female lung cancer and for non-Hodgkin’s lymphoma, both of which increased.

Howe, a researcher with the North American Association of Central Cancer Registries, said prostate cancer rates have fallen dramatically, by about a third over six years, while rates for lung and colon-rectum cancers either decreased slightly or stabilized.

The study compares the rate of cancer incidence and death in the United States from 1992 to 1998 with similar statistics from earlier years. It is the result of combined data and analysis from the National Cancer Institute, the Centers for Disease Control and Prevention, the American Cancer Society and the NAACCR.

“This welcome news on declining rates underscores the incredible progress we’ve made against cancer, but it also reminds us that our fight is far from over,” Health and Human Services Secretary Tommy G. Thompson said.

While cancer deaths declined across the whole population, the study found, overall cancer incidences declined only for men while women experienced increases, driven by breast and lung cancers.

Female breast cancer rates have jumped by about 40 percent since 1973, when the incidence was 82.6 per 100,000. In 1998, the rate was 118.1. The average overall annual increase was 1.2 percent per year for the six years ending in 1998.

The breast cancer increase, said Howe, “is driven by an increase in screening by the age group at highest risk. When you have more screening, you will pick up more tumors.”

Most of the increase in breast cancer incidence was among women age 50 to 74, the age group at highest risk.

Howe said it is expected that increased screening – principally through mammography – will eventually result in fewer breast cancer deaths.

“As we detect cancers earlier, we would expect there to be a decline in mortality,” she said.

The study found that breast cancer death rates declined by 2.4 percent annually from 1992 to 1998.

Cancers of the lung, thought to be caused primarily by cigarette smoking, continue to be the most lethal of the cancers, accounting for 28.5 percent of all cancer deaths.

The study found that lung cancer incidence among women is declining, but death from the disease among women is up slightly. New cases of the disease declined by 2.7 percent per year among men and by 0.2 percent per year among women between 1992 and 1998.

Lung cancer death rates among men declined by 1.9 percent per year, but rose by 0.8 percent per year among women.

Lung cancer death “is still increasing among women, but it is slowing down,” said Howe. In the 1970s and ’80s, the death rate among women was increasing by more than six percent a year, she noted.

Howe said the lung cancer death rate among women is following the pattern seen earlier among men, where the death rate started dropping as older smokers died and fewer young people started smoking.

“Since women started smoking at a later age, we are still approaching the peak of lung cancer” among them, said Howe.

Colon-rectum cancer rates across the whole population dropped by 0.7 percent a year from 1992 to 1998, with a 1.3 percent per year decline among white men and 1.1 percent among black men. The decline was 0.4 percent per year for white women, 0.3 percent for black women.

Death rates from colon-rectum cancer dropped dramatically for white men, by 2.3 percent per year, but less so for black men, 0.9 percent per year. Among white females, the colon-rectum cancer death rate dropped by 1.9 percent per year. For black females it was down by 0.6 percent per year from 1992 to 1998.

Death from melanoma, which accounted for 1.4 percent of all cancer deaths, increased by 1 percent per year among white males, while remaining stable among white females from 1992 to 1998. New cases increased by 2.7 percent per year among white men and 2.9 percent among white females. Melanoma is a skin cancer linked to excessive sun exposure.